1. Field of the Invention
The present invention relates to a burner for industrial and household use having a wide range of adjustability in terms of the quantity of heat for a given quantity of fuel supplied, i.e., a wide range of the turn-down ratio (the ratio of the minimum fuel flow relative to the rated fuel flow).
2. Description of the Prior Art
A partial premixing type burner is currently widely used as an industrial burner and a household burner. In the partial premixing type burner, it is well known that an air-fuel mixture is ignited at burner ports to form premixed flames which in turn bring about diffusion flames when a secondary air is supplied into the premixed flames from the surroundings of the premixed flames. On the other hand, in a Smithells burner, the premixed flames and the diffusion flames are separated while a secondary air is supplied from the surroundings of the diffusion flames.
However, with the burner of a type wherein the diffusion flames are formed around the premixed flames, it has often been observed that, when the quantity of heat is low or when the excess air ratio of the premixed gas approaches 1, the burner tends to exhibit an abrupt increase in temperature to such an extent as to result in back-firing. When the amount of air in the premixed gas is increased to increase the excess air ratio, or when the amount of fuel is increased to increase the flow rate of the fuel, the flames tend to become unstable, the burner tends to emit a relatively large amount of unburned components of the air-fuel mixture and flame blow-off tends to occur. Because of this, the adjustable range of the quantity of heat and that of the air are so small as to be inconvenient in use.
On the other hand, with the Smithells burner, there has been found a problem in that, where the excess air ratio of the premixed gas is greater or smaller than 1, the premixed flames tend to become unstable.